Scaffolds with trace element for tissue regeneration in mammals

ABSTRACT

A scaffold for implantation into a mammal to facilitate vessel growth in repair, regeneration, and/or proliferation of bodily tissue, where the scaffold is based on a borate, silicate, or phosphate, glass-former and is biodegradable upon implantation in mammals. The scaffold includes one or more trace elements from the group consisting of Cu, F, Fe, Mn, Mo, Ni, Sr, and Zn which are released into the host to support vessel growth. A method involves implantation of such scaffolds.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Department of theArmy contract W81XWH-08-1-7065. The Government may have certain rightsin the invention.

FIELD OF THE INVENTION

This invention relates to biocompatible compositions for surface andsubsurface implantation into mammals to facilitate tissue repair,regeneration, and proliferation.

BACKGROUND OF THE INVENTION

Silicate-based glasses have been used as a basis for implantablecompositions to support the bonding, growth or genesis of bone byfostering a supportive environment between the material and living, boneprogenitor cells. It is widely recognized that successful bioactiveglasses include calcium and silica in order to foster the neededsupportive environment. Certain of these compositions are consideredbioactive since they possess surfaces capable of fostering a calciumphosphate layer which, in turn, promotes bone bonding to the material.For example, U.S. Pat. No. 5,204,106 discloses a composition termed 45S5glass which is composed of Na₂O—CaO—P₂O₅—SiO₂.

Day et al. U.S. Pat. No. 6,709,744 describes biocompatible materials forimplantation which include borate-based glass or ceramic materialscontaining Na₂O, CaO, P₂O₅, and B₂O₃. A specific example is a glasscontaining about 22.9 wt % Na₂O, about 22.9 wt % CaO, about 5.6 wt %P₂O₅, and about 48.6 wt % B₂O₃. These materials contain a high CaOconcentration to facilitate the formation of hydroxyapatite when exposedto phosphorus-containing fluids in-vivo or prior to implantation. Thesematerials are in the form of loose particulates which are looselypacked, for example in a glass capillary tube for release into a host.Liang et al., Bioactive Borate Glass Scaffold for Bone TissueEngineering, J. Non-Crystalline Solids 354 (2008), p. 1690-96; and Yaoet al., In-Vitro Bioactive Characteristics of Borate-Based Glasses withControllable Degradation Behavior, J. Am. Cer. Soc. 90 (2007), p.303-306 also disclose borate-based glasses formulated with high CaO forthe formation of hydroxyapatite. For example, the 0B, 1B, 2B, and 3Bglasses described by Yao et al. contain 0, 17.7, 35.4, and 53 wt %borate.

There is a continuing need for biocompatible materials which promoterapid repair of mammalian tissue, and especially for enhancingvascularity.

SUMMARY OF THE INVENTION

Briefly, therefore, the invention is directed to a scaffold forimplantation into a mammal to facilitate vessel growth in repair,regeneration, and/or proliferation of bodily tissue, the scaffoldcomprising: a scaffold body of biocompatible material in a physical formselected from the group consisting of fibers, hollow fibers, tubes,ribbons, solid spheres, hollow spheres, particles, bonded particles, andcombinations thereof; wherein the biocompatible material comprises fromabout 40 to about 80 wt % B₂O₃; and wherein the biocompatible materialcomprises one or more trace elements selected from the group consistingof Cu, Fe, Sr, and Zn chemically dissolved in the biocompatible materialin a concentration between about 0.05 and 10 wt %.

In another aspect, the invention is directed to a scaffold forimplantation into a mammal to facilitate vessel growth in repair,regeneration, and/or proliferation of bodily tissue, the scaffoldcomprising: a scaffold body comprising biocompatible material in aphysical form selected from the group consisting of fibers, hollowfibers, tubes, ribbons, solid spheres, hollow spheres, particles, bondedparticles, and combinations thereof which biocompatible materialcomprises a glass former selected from the group consisting of B₂O₃,SiO₂, P₂O₅, and combinations thereof, and which is biodegradable inmammalian bodily fluids; and one or more trace elements selected fromthe group consisting of Cu, F, Fe, Mn, Mo, Ni, Sr, and Zn chemicallydissolved in the biocompatible material in a concentration between about0.05 and 10 wt %; wherein said glass formers are concentration balancedto impart a biodegradability such that at least about 20 wt % of thebiocompatible material biodegrades within six weeks of subcutaneousimplantation in a Fisher 344 rat having an age between 9 and 11 weeksand a weight between 200 and 300 grams, as determined by testing on ratswith a standard deviation of 25% (relative) of the biocompatiblematerial weight and a population size of 10.

In another aspect the invention is directed to a method for facilitatingvessel growth in repair, regeneration, and/or proliferation of bodilytissue in a mammal involving implantation of these scaffolds.

Other objects and features of the invention are in part apparent and inpart pointed out hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a series of photographs of scaffolds according to an Example.

FIGS. 2, 3, and 4 each contain a series of photographs of scaffolds ofFIG. 1 after implantation.

FIGS. 5 through 7 are photographs of scaffolds after implantation,removal, sectioning, and staining for histology (H&E).

FIG. 8 is a graph depicting angiogenesis as a function of CuO content inbiocompatible materials of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with this invention, a trace element such as B, Cu, F, Fe,Mn, Mo, Si, Sr, and/or Zn is incorporated into a scaffold of abiocompatible composition which is implantable at a mammal's surface orsubsurface. The scaffold composition provides ions for biological use bythe mammal. These elements have beneficial effects such as an effect onendothelial cell migration which can be useful for blood vesselformation and have importance for tissue regeneration. In this way,these trace elements promote angiogenesis, which is a critical functionin promoting tissue growth, such as in wound healing. This is indistinction from promoting osteoconductivity, which refers to providingbone growth factors to a site to promote bone growth. Angiogenesis,which involves increasing vascularity, i.e., vessel growth, is distinctfrom osteoconductivity.

The scaffold of the invention comprises a scaffold body comprising abiocompatible material in the form of one or more of fibers, hollowfibers, tubes, ribbons, solid spheres, hollow spheres, particles, bondedparticles, and combinations thereof. In many of the more preferredembodiments, the form is loose or bonded fibers, or bonded particles.Generally speaking, the scaffold has a weight of at least about 10milligrams, such as between about 10 milligrams and about 500 grams, forexample between about 20 milligrams and about 2500 milligrams. Thebiocompatible material is borate-based, phosphate-based, and/orsilicate-based and is glass, crystalline, or a combination of glass andcrystalline.

The biocompatible material fibers, spheres, or other-shaped componentsin some embodiments are in a loose assembly of nonbonded components.Alternatively, they are bonded to each other, typically by heating, todefine a scaffold body and provide a scaffold body compressive strengthof greater than 0.4 MPa. The desired compressive strength is selected sothat the components are in no sense free flowing, and so that thescaffold body can be handled without disintegrating into the individualbody components. The desired compressive strength is also selected toprovide the strength that is required to remain integral afterimplantation, whether for repair of a load-bearing body part ornon-load-bearing part, or one subject to impact or significant movement.In some preferred embodiments, the compressive strength of the scaffoldbody is at least about 5 MPa, while in other embodiments where greaterrigidity is required, the compressive strength is at least about 20 MPa,such as between about 20 and about 200 MPa.

The initial surface area of the scaffold varies widely depending on thescaffold morphology—for example, whether it is all fibers, the fiberdimensions, whether it is particles, the particle size, etc. Moreover,the surface area changes during biodegradation. Generally speaking,scaffolds of the fibrous morphology and generally of the dimensions inbelow Example 1 have a surface area/bulk scaffold volume of betweenabout 50 and about 1000 cm⁻¹, such as between about 50 and about 500cm⁻¹. The scaffold in Example 1 has a surface area/unit bulk volume of134 cm⁻¹, based on its dimensions of being a cylinder 7 mm in diameterand 2 mm high. The surface area of the starting glass fibers was 10.27cm² and the bulk volume of the cylinder was 7.7×10⁻²,cm³.

One or more selected trace elements are incorporated into theimplantable material in a concentration of at least about 0.05 wt %, orat least about 0.1 wt %. In most instances, the concentration is lessthan 10 wt %, or less than 5 wt %, such as between about 0.05 and about5 wt %, for example between about 0.1 and about 2.5 wt % (per element).Where the implantable biocompatible material is borate-based orphosphate-based, the trace element concentration is less than 5 wt %,and it may be higher and up to 10 wt % where the biocompatible materialis silicate-based. The trace elements are selected from the groupconsisting of B, Cu, F, Fe, Mn, Mo, Ni, Si, Sr, and Zn. In certainpreferred embodiments the trace element is one or more selected from thegroup consisting of Cu, F, Fe, Mn, Mo, Sr, and Zn. In some especiallypreferred embodiments for certain applications, the trace element is oneor more selected from the group consisting of Cu, Fe, Sr, and Zn. Morethan one of these trace elements can be employed in a singlecomposition. Silicon as a trace element is applicable to borate-basedand phosphate-based glasses, and not to silicate-based glasses. Boron asa trace element is applicable to silicate-based and phosphate-basedglasses, and not to borate-based glasses. Accordingly, the group of Cu,F, Fe, Mn, Mo, Sr, and Zn has more general applicability. Also, certainof these elements may be present in greater amounts in that they are notbeing used as trace elements in accordance with this invention. Forexample, a scaffold made of a biocompatible glass material whichcontains 0.4 wt % Cu and 15 wt % Sr contains Cu as a trace element inaccordance with this invention; and it contains Sr, but not as a traceelement in accordance with this invention. Such a material would indeedsatisfy the requirement herein for a trace element from the group Cu, F,Fe, Mn, Mo, Ni, Sr, and Zn in a concentration between about 0.05 and 10wt % by virtue of the material's Cu content, regardless of itsunqualifying Sr content.

Where Cu is desired, the source of Cu to the glass or crystallinebiocompatible material may be a copper oxide such as CuO or Cu₂O orother copper compounds such as copper nitrate or copper sulfate, forexample. In one embodiment, Cu is incorporated into the glass in aconcentration of between about 0.05 and about 5 wt % (about 0.06-6 wt %CuO; about 0.055-5.5 wt % Cu₂O), such as between about 0.1 and about 2.5wt % (about 0.12-3 wt % CuO; about 0.11-3 wt % Cu₂O). There arepreferred embodiments employing from about 1 wt % to about 2 wt % Cu, asprovided by between about 1.2 wt % and about 2.4 wt % CuO.

Where Sr is desired, the source of Sr to the glass or crystallinebiocompatible material may be an oxide such as SrO or other Sr compoundssuch as SrCO₃, for example. In one embodiment, Sr is incorporated intothe glass in a concentration of between about 0.05 and about 5 wt %(about 0.06 to 5.90 wt % SrO), such as between about 0.1 and about 2.5wt % (about 0.12 to 2.95 wt % SrO). There are preferred embodimentsemploying from about 1 wt % to about 2 wt % Sr, as provided by betweenabout 1.18 wt % and about 2.36 wt % SrO.

Where Zn is desired, the source of Zn to the glass or crystallinebiocompatible material may be an oxide such as ZnO or other Zn compoundssuch as Zn₃(PO₄)₂-xH₂O, for example. In one embodiment, Zn isincorporated into the glass in a concentration of between about 0.05 andabout 5 wt % (about 0.06 to 6.0 wt % ZnO), such as between about 0.1 andabout 2.5 wt % (about 0.12 to 3.0 wt % ZnO). There are preferredembodiments employing from about 1 wt % to about 2 wt % Zn, as providedby between about 1.20 wt % and about 2.40 wt % ZnO.

Where Fe is desired, the source of Fe to the glass or crystallinebiocompatible material may be an oxide such as FeO, Fe₃O₄, Fe₂O₃, orother Fe compounds such as FeSO₄-7H₂O, for example. In one embodiment,Fe is incorporated into the glass in a concentration of between about0.05 and about 5 wt % (about 0.06 to 6.45 wt % FeO), such as betweenabout 0.1 and about 2.5 wt % (about 0.13 to 3.23 wt % FeO). There arepreferred embodiments employing from about 1 wt % to about 2 wt % Fe, asprovided by between about 1.29 wt % and about 2.58 wt % FeO.

The trace element and biocompatible composition are carefully selectedand formulated to provide a specifically timed release of trace elementbased on flow of blood or other physiological fluids through thescaffold as the biocompatible composition biodegrades in the mammalianhost. The trace element is an integral component of the biocompatiblecomposition and is chemically dissolved in the material. This is insharp contrast to being in the form of a coating on the glass or beingsimply adsorbed onto the material as, for example, adsorbed onto a waterinsoluble implantable compound. Since the trace element is chemicallydissolved in the glass material, it is released into the host mammalincrementally as the glass biodegrades, and over that same period duringwhich the glass biodegrades. In contrast, a coating or adsorbed materialis released more quickly, and its release cannot be controlled bycontrolling the composition of the overall glass material. In oneembodiment, the trace element is generally macro-homogeneously presentin the biocompatible composition to facilitate release over the entiredegradation life of the composition. As blood and or other fluids flowthrough the scaffold and the scaffold biodegrades in the host mammal,the trace element is released to provide its advantageous angiogeniceffect over time in promoting benefits to the host in the area of theimplantation. So, for example, as the borate-based, phosphate-based, orsilicate-based composition biodegrades, it releases trace element topromote angiogenesis.

The glass formers in certain embodiments of the invention areconcentration balanced to impart the desired biodegradability. Forexample, in the B3-Cu1 composition of below Example 1, theconcentrations of the glass formers borate, silicate, and phosphate arebalanced to 52.95 wt %, 0 wt %, and 4.0 wt %, respectively, with respectto themselves and with respect to the other components in the materialNa₂O, CaO, and K₂O. Balancing in this regard encompasses balancing theconcentration of one glass former with other components, such as withthose glasses in Table 3 which contain borate and other components, butno phosphate or silicate.

In many preferred embodiments of the scaffold, the concentrations ofglass formers are balanced such that at least about 20 wt % of thebiocompatible material biodegrades within six weeks of implantation inits mammalian host. For example, the concentrations of glass formers arebalanced such that at least about 20 wt % of the biocompatible materialbiodegrades within six weeks of implantation in a Fisher 344 rat havingan age between 9 and 11 weeks and a weight between 200 and 300 grams. Inaccord with this measure, the testing is performed on rats with astandard deviation of 25% (relative) of the biocompatible material and apopulation size of 10. In other words, when 10 of these scaffolds areimplanted into the subcutaneous sites of rats, on average at least 20 wt% of the scaffolds' material biodegrades within six weeks; and in atleast 68% of rats at least 15 wt % of the scaffold biodegrades; and inat least 90% of rats at least 10 wt % of the scaffold degrades.Implantation for this and the following standards is according to theprotocol described below in Example 1. Biodegrading in most instancesmanifests itself either as scaffold weight loss, but can also manifestitself as another reaction of the scaffold material involving a changeof composition which results in release of trace element into the host.

Similarly, in another aspect, the concentrations of glass formers arebalanced such that at least about 20 wt % of the trace elementconcentration in the scaffold is released from the scaffold into thehost within six weeks of implantation in its mammalian host. Forexample, the concentrations of glass formers are balanced such that atleast about 20 wt % of the trace element concentration in the scaffoldis released from the scaffold into the host within six weeks ofimplantation in a Fisher 344 rat having an age between 9 and 11 weeksand a weight between 200 and 300 grams. In accord with this measure, thetesting is performed on rats with a standard deviation of 25% (relative)of the biocompatible material and a population size of 10. In otherwords, when 10 of these scaffolds are implanted into the subcutaneoussites of rats, on average at least 20 wt % of the scaffolds' traceelement concentration is released within six weeks; and in at least 68%of rats at least 15 wt % of the scaffolds' trace element concentrationis released; and in at least 90% of rats at least 10 wt % of thescaffolds' trace element concentration is released.

On the other hand, the scaffold does not biodegrade so quickly in thehost that it fails to provide trace elements over a long enough periodto adequately promote angiogenesis. For example, at least 50 wt % of thescaffold material remains for at least two weeks and does not biodegradewithin two weeks. That is, the concentrations of glass formers arebalanced such that at least about 50 wt % of the biocompatible materialremains for at least two weeks after implantation in a Fisher 344 rathaving an age between 9 and 11 weeks and a weight between 200 and 300grams. In accord with this measure, the testing is performed on ratswith a standard deviation of 25% (relative) of the biocompatiblematerial and a population size of 10. In other words, when 10 of thesescaffolds are implanted into the rats, on average at least 50 wt % ofthe scaffolds' material does not biodegrade within two weeks; and in atleast 68% of rats at least 37.5 wt % of the scaffold does not biodegradewithin two weeks; and in at least 90% of rats at least 25 wt % of thescaffold does not biodegrade within two weeks.

Moreover, in these embodiments, at least 50 wt % of the scaffold traceelement concentration remains for at least two weeks. That is, theconcentrations of glass formers are balanced such that at least about 50wt % of the trace element remains for at least two weeks afterimplantation in a Fisher 344 rat having an age between 9 and 11 weeksand a weight between 200 and 300 grams. In accord with this measure, thetesting is performed on rats with a standard deviation of 25% (relative)of the biocompatible material and a population size of 10. In otherwords, when 10 of these scaffolds are implanted into the rats, onaverage at least 50 wt % of the scaffolds' trace element concentrationremains for at least two weeks; and in at least 68% of rats at least37.5 wt % of the scaffolds' trace element concentration remains for atleast two weeks; and in at least 90% of rats at least 25 wt % of thescaffolds' trace element concentration remains for at least two weeks.

In one embodiment of the invention the biocompatible compositionreleases the trace element at particular rate of release of traceelement, per gram of glass, per day in a mammalian host. The releaserate can in effect be “dialed in” by determining the desired amount oftrace element to be released within the host, and then selecting abiocompatible composition or combination of compositions to achieve thisrate. As noted above, the glass formers are concentration balanced toimpart the desired biodegradability. In a related aspect, the surfacearea per unit volume can be controlled to control release rate, asgreater surface area increases reactivity and therefore release rate.One skilled in the art appreciates that the rate of biodegradation ofthe glass material is different from host to host, from glass to glass,from trace element to trace element, and otherwise depends on a numberof factors. For example, a more physically active host with a fasteraverage heart rate may encourage biodegradation and therefore traceelement release at a faster rate. In one embodiment, the composition hasa trace element release (Cu) rate of between about 0.5 and about 100 E-7moles of trace element, per gram of glass, per day; for example, betweenabout 1 and about 25 E-7 moles of trace element, per gram of glass, perday; such as between about 1 and about 20 E-7 moles of trace element,per gram of glass, per day, or between about 3 and about 12 E-7 moles oftrace element, per gram of glass, per day.

As an alternative perspective on trace element release for thisinvention, in one embodiment for certain applications, the rate ofrelease is between about 0.1 and about 60 micromolar; i.e., betweenabout 0.1 and about 60 micromoles trace element are released per literof flow through the composition. In other embodiments, the compositionis formulated to provide a release rate of between about 0.5 and about30 micromolar, such as between about 3 and about 12 micromolar. Forexample, in one embodiment where the trace element is Cu and thecomposition is a borate-based or silicate-based scaffold, the scaffoldcomposition is prepared to yield a Cu release rate during blood flowtherethrough of between about 0.1 and about 60 micromolar, such asbetween about 0.5 and 30 micromolar, or between about 3 and about 12micromolar.

As noted above, the biocompatible materials of the inventive scaffoldsbiodegrade in physiological fluids. However, in comparison to articlescharacterized as “water soluble” which dissolve relatively rapidly (overa period of, e.g., three weeks or less) in aqueous solutions, thebiocompatible materials of the invention are not water soluble, that is,they are resistant to rapid water solubility. For example, scaffoldsmade from them having a surface area and size of practical applicationfor use as an implantable scaffold do not completely dissolve in a lessthan several weeks (e.g., six weeks) at 37° C. in an aqueous phosphatesolution or an aqueous solution with a miscible solvent such asmethanol, ethanol, isopropanol, acetone, ethers or the like. Asunderstood in the art, materials which are “water soluble” are subjectto relatively rapid solubility; and materials which are “waterinsoluble” are either entirely insoluble in water, or are at least onlydissolvable with difficulty. Generally speaking the scaffolds materialsare not water insoluble and are not water soluble under thischaracterization; rather, they are of intermediate water solubility.

The material is biocompatible in that it is not toxic or otherwiseharmful to its host's living tissue. Some of the preferred compositions(Ca-free) of the invention are also not bioactive, in the sense thathydroxyapatite does not form. That is, they lack bioactivity, wherebioactivity refers to a material's capacity in phosphorus-containingmammalian fluids to foster growth of a calcium phosphate layer orconvert to bone-precursor calcium phosphate compounds which, in turn,promotes bone bonding to the material.

In one embodiment the biocompatible material into which the traceelement is incorporated is a borate-based glass material containing thefollowing, approximately, with all percentages herein being by weight,unless stated otherwise:

B₂O₃ 40 to 80 Na₂O 0 to 25 Li₂O 0 to 25 K₂O 0 to 25 Rb₂O 0 to 25 CaO 0to 40 MgO 0 to 25 SrO 0 to 40 BaO 0 to 50 Li₂O + Na₂O + K₂O + Rb₂O 0 to50 cumulative MgO + SrO + BaO + CaO 0 to 50 cumulative P₂O₅ 0 to 10 SiO₂0 to 18 Al₂O₃ 0 to 3 F 0 to 4 transition metal elements 0 to 10cumulative.The concentrations of K₂O and MgO in certain of these embodiments areeach from about 1 to about 25 wt %. In most embodiments, the one or moreof Li₂O, Na₂O, K₂O, and Rb₂O is present in a cumulative concentrationbetween about 1 and about 50 wt %, such as between about 5 and about 20wt %; and the one or more of MgO, SrO, BaO, and CaO is present in acumulative concentration between about 1 and about 50 wt %, such asbetween about 5 and about 40 wt %. Where Cu is the trace element, thiscomposition further contains 0.05 to 5; or 0.01 to 2.5 wt % Cu; as CuO,Cu₂O, or other Cu compound. The transition metal elements are thoseelements where the d-band contains less than its maximum number of tenelectrons per atom, and includes, among others, Co and Ni. In fact,certain of the trace elements used in accordance with this inventionsuch as Zn and Fe are transition metals. So in formulations where thetrace element concentration of these trace elements is stated to be in aparticular range such as between about 0.1 and about 2.5 wt %, of coursethe trace element concentration is in that range regardless of the factthat transition elements may be among the trace elements, and if Zn andFe are present in an amount greater than 2.5 wt %, they are not traceelements.

A few exemplary glass materials of the invention are as follows:

TABLE 1 Trace-Element-Containing Borate Biocompatible Glasses (wt %)Glass B₂O₃ Na₂O CaO K₂O MgO P₂O₅ CuO SrO ZnO Fe₂O₃ 1 52.95 5.99 19.9811.99 5.00 4.00 0.10 2 52.89 5.99 19.96 11.98 4.99 3.99 0.20 3 52.795.98 19.92 11.95 4.98 3.98 0.40 4 52.47 5.94 19.80 11.88 4.95 3.96 1.005 51.94 5.88 19.60 11.76 4.90 3.92 2.00 6 51.73 5.86 19.52 11.71 4.883.90 0.40 2.00 7 51.20 5.80 19.32 11.59 4.83 3.86 0.40 2.00 1.00 8 50.885.76 19.20 11.52 4.80 3.84 0.40 2.00 1.00 0.40

In most embodiments the biocompatible material consists only oressentially of components meeting these compositional requirements orother narrower descriptions herein. But generally speaking, for someembodiments other materials not meeting these descriptions may beincorporated into the scaffolds.

Additional borate-based materials within this description, into which Cuor other stated trace element may be incorporated according to thisinvention, contain, by weight %, the following, keeping in mind that oneor more of the other trace elements may be included in addition to Cu inanalogous concentrations, or instead of Cu:

TABLE 2 Wt. % Composition of Additional Borate Glasses B₂O₃ Na₂O K₂OLi₂O CaO BaO MgO P₂O₅ CuO A 52.5  6.0 12.0 20.0  5.0 4.0 0.5 B 70.3 10.319.3 0.1 C 63.7 19.0 17.2 0.1 D 49.0 14.6 36.0 0.4 E 78.4 11.5 10.0 0.1F 69.9 10.0 10.0 10.0 0.1 G 78.6 11.3 10.0 0.1 H 78.6 11.3 10.0 0.1 I75.9 11.0 13.0 0.1 J 58.6  8.0 33.0 0.4

It can therefore be appreciated that in addition to the Cu, and/or inaddition to Sr, Zn, Fe, Mn, F, Si, Ni, and/or Mo, the borate-basedbiocompatible materials include 40 to 80 wt % B₂O₃ or 50 to 80 wt %B₂O₃, or even the narrower B₂O₃ ranges described herein, in combinationwith 1 to 25 wt % Na₂O, 1 to 25% K₂O, 1 to 40 wt % CaO, 1 to 25 wt %MgO, and 1 to 10 wt % P₂O₅. Or the component materials may contain 40 to80 wt % B₂O₃, 1 to 25 wt % Li₂O, and 1 to 40 wt % CaO. Or they maycontain 40 to 80 wt % B₂O₃, 1 to 25 wt % Na₂O, and 1 to 40 wt % CaO. Orthey may contain 40 to 80 wt % B₂O₃, 1 to 25 wt % Na₂O, and 1 to 40 wt %BaO. Or they may contain 40 to 80 wt % B₂O₃, 1 to 25 wt % Li₂O, and 1 to25 wt % MgO. Or they may contain 40 to 80 wt % B₂O₃, 1 to 25 wt % Li₂O,and 1 to 40 wt % BaO. While the biocompatible materials hereinabove andhereinbelow are described as containing various oxides by weight %,those skilled in the art understand that in the final glass orglass/crystalline composition, the oxide compounds are dissociated, andthe specific oxides, e.g., B₂O₃, SiO₂, P₂O₅, etc. are not separatelyidentifiable or even necessarily separately present. Nonetheless, it isconventional in the art to refer to the final composition as containinga given % of the individual oxides, so that is done here. So from thisperspective, the compositions herein are on an equivalent basis.

The biocompatible materials of the invention containing the traceelement in certain preferred versions are borate-based in that theycontain between about 40 and about 80 wt % B₂O₃, such as between about50 and about 80 wt % B₂O₃. Borate-based materials have several importantadvantages for biological use such as their ease of preparation, abilityto be made into glass particulates, microspheres or fibers at relativelylow temperatures without crystallization, and, particularly, theirbiocompatibility. The borate-based materials disclosed herein, comparedto silicate-based materials, have significantly faster reaction rates,lower melting temperatures, resistance to crystallization, and incertain instances the absence of silica, which only slowly degrades inthe body. So while certain embodiments employ up to about 18 wt % SiO₂in many other preferred embodiments herein, the materials aresilicate-free, containing less than 0.1 wt % silicate or even nosilicate. Borate glasses form hollow fibers upon reaction in-vivo, whilesilicate glasses do not; and they facilitate angiogenesis in-vivo. Theborate materials described herein also release boron in-vivo as theyreact with the body fluids.

There is one embodiment which has specific preference in certainapplications and wherein the concentration of Ca (elemental or in CaO orother compounds) in the material is controlled to less than about 5 wt%. Certain preferred embodiments strictly control the Ca concentrationto less than about 0.5 wt %, such as to less than 0.2 wt %, and even toless than 0.1 wt %. The advantage in this embodiment to strictlycontrolling Ca concentration is the avoidance of the formation ofcalcium phosphate compounds, apatite type compounds and relatedamorphous calcium phosphate (ACP) upon exposure to physiologicalphosphorus-containing fluids. Such apatite compounds includehydroxyapatite Ca₅(PO₄)₃(OH), fluoroapatite Ca₅(PO₄)₃F, amorphouscalcium phosphate (ACP), and other calcium-containing compounds. Thus,in certain applications it is advantageous to avoid the formation ofCa-apatite compounds because they have a relatively lower radiopacitythan do, for example, analogous Sr or Ba compounds. In certainsituations it is advantageous to avoid Ca-apatite compounds in order toform compounds which degrade more rapidly, or perhaps even more slowly.It can also be advantageous to avoid Ca for purposes of controlling meltcharacteristics, such as viscosity, melting temperature, and/orcrystallization tendency. The Ca-free compositions lack bioactivity,where bioactivity refers to a material's capacity inphosphorus-containing mammalian fluids to foster growth of a calciumphosphate layer or convert to bone-precursor calcium phosphatecompounds.

The biocompatible Ca-free material in one embodiment into which the Cuand/or other trace element is incorporated in the concentrationsdescribed above preferably contains between about 40 and about 80 wt %B₂O₃ with the remainder being selected from alkali oxides and alkalineearth oxides, and other optional constituents listed below. For example,this material contains, by weight %:

B₂O₃ 40 to 80 Na₂O 0 to 25 Li₂O 0 to 25 K₂O 0 to 25 Rb₂O 0 to 25 MgO 0to 25 SrO 0 to 40 BaO 0 to 25 Li₂O + Na₂O + K₂O + Rb₂O 0 to 50cumulative MgO + SrO + BaO 0 to 50 cumulative P₂O₅ 0 to 10 SiO₂ 0 to 18Al₂O₃ 0 to 3 F 0 to 4 transition metal elements 0 to 10 cumulative.In addition, the material contains Cu in a concentration of 0.05 to 5;or 0.01 to 2.5 wt %, as CuO, Cu₂O, or other Cu compound, and/or othertrace element. Certain of these embodiments contain low levels of Ca, asdescribed above; while others are substantially Ca-free and containessentially no or less than 0.1 wt % Ca.

In one preferred embodiment, the material contains between about 50 andabout 80 wt % B₂O₃; between about 5 and about 20 wt % alkali oxidecomponent selected from the group consisting of Li₂O, Na₂O, K₂O, Rb₂O,and combinations thereof; and between about 5 and about 40% alkalineearth component selected from the group consisting of MgO, SrO, BaO, andcombinations thereof. Lanthanides are specifically and strictly excludedfrom certain preferred embodiments. In some embodiments thebiocompatible material consists essentially of between about 50 andabout 80 wt % B₂O₃; between about 5 and about 20 wt % alkali oxidecomponent selected from the group consisting of Li₂O, Na₂O, K₂O, Rb₂O,and combinations thereof; between about 5 and about 40 wt % alkalineearth component selected from the group consisting of MgO, SrO, BaO, andcombinations thereof, and between about 0.05 and 5 wt % Cu, as CuO,Cu₂O, or other Cu compound

Exemplary borate-based Ca-free materials, into which Cu may beincorporated according to this invention, contain, by weight %, thefollowing, keeping in mind that one or more of the other trace elementsmay be included in addition to Cu in analogous concentrations, orinstead of Cu:

TABLE 3 Wt. % Composition of Ca-Free Borate Glasses B₂O₃ Na₂O Li₂O MgOBaO CuO I 49.0 14.6 36.1 0.3 II 78.7 11.1 10.0 0.2 III 78.7 11.1 10.00.2 IV 75.8 11.0 13.0 0.2 V 58.7  8.0 33.0 0.3 VI 45.0  6.6 48.0 0.4 VII69.7 10.0 10.0 10.0 0.3

In certain embodiments of the invention, the biocompatible material isselected to include at least two of the alkali oxides Li₂O, Na₂O, K₂O,and/or Rb₂O in a cumulative concentration of between about 5 and about25 wt %, such as between about 8 and 20 wt %. It has been discovered tobe advantageous to include two or more such alkali compounds in order toreduce the tendency for crystallization, which ultimately improves theworkability and manufacturability of the glasses, which can important tomaking scaffolds. Using more than one type of alkali (i.e., mixedalkali) can reduce the cost of a glass, modify its reaction rate withbody fluids, and provide additional elements beneficial to tissue growthand regeneration.

A further feature of certain embodiments is that the cumulativeconcentration of the alkaline earth oxides from the group consisting ofMgO, SrO, BaO, CaO, and combinations thereof is in the range of 1 toabout 50 wt %, such as in the range of 1 to 30 wt %, or even about 8 to25 wt %. Certain of these embodiments contain two or more such alkalineearth oxides in a range of 1 to 45 wt % cumulatively, such as in therange of 5 to 25 wt %. If SrO is present in a concentration which yieldsa Sr concentration above 10 wt %, it does not qualify as a trace elementin accordance with this invention.

These embodiments into which Cu and/or other trace element may beincorporated and which employ mixed alkali oxide contents contain B₂O₃from about 40 to about 80 wt %. Certain of these embodiments consistessentially of B₂O₃ from about 40 to about 80 wt %, mixed alkali oxidesselected from the group consisting of Li₂O, Na₂O, K₂O, and Rb₂O, and oneof MgO, SrO, BaO, or CaO, plus the Cu containing compound. Otherembodiments consist essentially of B₂O₃ from about 40 to about 80 wt %,two or more alkali oxides selected from the group consisting of Li₂O,Na₂O, K₂O, and Rb₂O, and two or more alkaline earth oxides from thegroup consisting of MgO, SrO, BaO, and CaO, plus the Cu containingcompound. For example, composition A in Table 2 consists essentially ofB₂O₃ from about 40 to about 80 wt %, two or more mixed alkali oxidesselected from the group consisting of Li₂O, Na₂O, K₂O, and Rb₂O in acumulative wt % between 5 and 25%, and two or more from among MgO, SrO,BaO, and CaO in a cumulative wt % between 8 and 25%. Other embodimentsoptionally include one or more of P₂O₅, SiO₂, Al₂O₃, F, and transitionmetal elements.

The invention includes incorporating Cu and/or other trace element intobiocompatible materials with an especially high B₂O₃ composition,namely, from about 60 to about 82 wt %, still more preferably from about70 to about 80 wt %. These embodiments employ an alkali oxide selectedfrom the group consisting of Li₂O, Na₂O, K₂O, Rb₂O, and combinationsthereof cumulatively from about 1 to about 50 wt %, such as from about 5to about 25 wt %, and even from about 8 to about 20 wt %; and evenoptionally two or more such oxides cumulatively in this range. They alsooptionally employ alkaline earth oxides from group consisting of MgO,SrO, BaO, CaO, and combinations thereof in the range of about 1 to about50 wt %, such as in the range of 1 to 30 wt %, or even about 8 to 25 wt%, and even two or more such oxides cumulatively in this range. Certainof these embodiments consist essentially of these components, such ascompositions II, III, IV, and VII in Table 3; while other embodimentsoptionally include one or more of P₂O₅, SiO₂, Al₂O₃, F, and transitionmetal elements.

In the foregoing described mixed-alkali and high-borate embodiments, theCa concentration may be strictly controlled to less than about 5 wt %,including to less than 0.5 wt %, such as to less than 0.2 wt % or lessthan 0.1 wt % to avoid the formation of Ca compounds, in the mannerdiscussed above. Alternatively, there are embodiments containing two ormore alkali oxides which also contain CaO in an amount up to about 40 wt% to facilitate the formation of hydroxyapatite, other calcium phosphatecompounds, amorphous calcium phosphate, or other calcium containingcompounds.

Some exemplary materials of the invention such as depicted in theworking examples contain, approximately, 40 to 80 wt % B₂O₃, 0.05 to 5%CuO, and Na₂O, K₂O, MgO, and P₂O₅. More specific examples contain oreven consist essentially of 40 to 80 wt % B₂O₃, 0.1 to 5% CuO, 1 to 25wt % Na₂O, 1 to 25 wt % K₂O, 1 to 25 wt % MgO, and 1 to 10 wt % P₂O₅.

The invention also encompasses a biocompatible composition forimplantation into a mammal to facilitate vessel growth in repair,regeneration, and/or proliferation of bodily tissue, wherein thebiocompatible material is phosphate-based or silicate-based and is atleast partially dissolvable in mammalian bodily fluids, and Cu isincorporated into the biocompatible material in a concentration asdescribed above. In these embodiments, P₂O₅ and/or SiO₂ are glassformers and constitute about 20 to about 65 wt % P₂O₅ or about 20 toabout 60 wt % SiO₂. These materials also contain an alkali metal oxidecomponent of, for example, one or more of Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O,or a mixture thereof in a concentration of about 8 wt % to about 55 wt%, such as about 10 to about 52 wt %. Many of these phosphate- andsilicate-based glasses also contain a calcium component, one of CaO,CaF₂, or mixtures thereof. For example, many of these glasses containfrom about 5 to about 40 wt % of CaO or CaF₂, or mixtures thereof, suchas about 10 to about 30 wt % of CaO or CaF₂, or mixtures thereof, orabout 10 to about 15 wt % of CaO or CaF₂, or mixtures thereof.Accordingly, one of these embodiments contains about 20 to about 65 wt %P₂O₅, and one or more of Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, or a mixturethereof in a concentration of about 8 wt % to about 55 wt %, and acalcium component of in a concentration of about 5 to about 40 wt % ofCaO or CaF₂, and Cu in a concentration of about 0.05 to about 5 wt %,such as between about 0.1 and about 2.5 wt %. Another embodimentcontains about 20 to about 65 wt % P₂O₅, and one or more of Li₂O, Na₂O,K₂O, Rb₂O, Cs₂O, or a mixture thereof in a concentration of about 10 wt% to about 52 wt %, a calcium component of CaO or CaF₂ or mixturesthereof in a concentration of about 5 wt % to about 40 wt % of CaO orCaF₂ or mixtures thereof, and Cu in a concentration of about 0.05 toabout 5 wt %, such as between about 0.1 and about 2.5 wt %. Anotherembodiment contains about 20 to about 65 wt % P₂O₅, and one or more ofLi₂O, Na₂O, K₂O, Rb₂O, Cs₂O, or a mixture thereof in a concentration ofabout 8 wt % to about 55 wt %, a calcium component of CaO or CaF₂ ormixtures thereof in a concentration of about 10 to about 30 wt % of CaOor CaF₂ or mixtures thereof, and Cu in a concentration of about 0.05 toabout 5 wt %, such as between about 0.1 and about 2.5 wt %. Another ofthese embodiments contains about 20 to about 60 wt % SiO₂, and one ormore of Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, or a mixture thereof in aconcentration of about 8 wt % to about 55 wt %, a calcium component ofCaO in a concentration of about 5 to about 40 wt % of CaO or CaF₂, andCu in a concentration of about 0.05 to about 5 wt %, such as betweenabout 0.1 and about 2.5 wt %. Another embodiment contains about 20 toabout 60 wt % SiO₂, and one or more of Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, or amixture thereof in a concentration of about 10 wt % to about 52 wt %, acalcium component of CaO or CaF₂ or mixtures thereof in a concentrationof about 5 wt % to about 40 wt % of CaO or CaF₂ or mixtures thereof, andCu in a concentration of about 0.05 to about 5 wt %, such as betweenabout 0.1 and about 2.5 wt %. Another embodiment contains about 20 toabout 60 wt % SiO₂, and one or more of Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, or amixture thereof in a concentration of about 8 wt % to about 55 wt %, acalcium component of CaO or CaF₂ or mixtures thereof in a concentrationof about 10 to about 30 wt % of CaO or CaF₂ or mixtures thereof, and Cuin a concentration of about 0.05 to about 5 wt %, such as between about0.1 and about 2.5 wt %. In certain of these embodiments, CaF₂ isstrictly avoided and the calcium component is CaO.

Examples of silicate-based biocompatible material containing Cu andother trace elements in accordance with this invention are as follows:

TABLE 4 Weight Percent Composition of Silicate-Based BiocompatibleGlasses (wt %) Glass SiO₂ Na₂O P₂O₅ CaO CuO FeO CaF₂ B₂O₃ ZnO MnO MgOK₂O A 44.6 24.3 5.9 24.3 1.0 B 44.1 24.0 5.9 24.0 2.0 C 43.7 23.8 5.823.8 3.0 D 43.2 23.5 5.8 23.5 4.0 E 42.8 23.3 5.7 23.3 5.0 F 44.0 25.06.0 20.0 0.2 0.2 1.0 2.2 0.6 0.2 0.6 G 50.0  6.0 19.0 0.2 0.2 1.0 3.01.0 0.2 12.0

Examples of phosphate-based biocompatible glass contain Cu in accordancewith this invention are shown in Table 5.

TABLE 5 Weight Percent Composition of Phosphate-Based BiocompatibleGlasses Glass ID Na₂O K₂O CaO MgO B₂O₃ P₂O₅ Li₂O SrO CuO P-1  3.8  5.827.5 2.5 0.0 60.0 0.0 0.0 0.4 P-2  9.2  9.3 27.5 0.0 0.0 53.5 0.0 0.00.5 P-3  7.8 11.8 17.0 7.6 0.0 55.2 0.0 0.0 0.6 P-4  7.8 11.8 17.0 7.60.0 55.2 0.0 0.0 0.6 P-5  6.6  8.9 21.9 0.0 4.1 58.0 0.0 0.0 0.5 P-610.5  0.0 23.0 0.0 4.0 61.1 1.1 0.0 0.3 P-7  8.0  3.7  1.5 0.0 1.8 78.10.0 6.7 0.2

These phosphate-based formulations demonstrate situations where it isadvantageous to include at least two of the alkali oxides Li₂O, Na₂O,K₂O, and/or Rb₂O in a cumulative concentration of between about 5 andabout 25 wt %, such as between about 8 and 20 wt %. As noted above, ithas been discovered to be advantageous to include two or more suchalkali compounds in order to reduce the tendency for crystallization,which ultimately improves the workability and manufacturability of theglasses, which can be important to making scaffolds. Using more than onetype of alkali (i.e., mixed alkali) can reduce the cost of a glass,modify its reaction rate with body fluids, and provide additionalelements beneficial to tissue growth and regeneration.

A further feature of these phosphate-based embodiments is that thecumulative concentration of the alkaline earth oxides from the groupconsisting of MgO, SrO, BaO, CaO, and combinations thereof is in therange of 1 to about 50 wt %, such as in the range of 1 to 30 wt %, oreven about 8 to 25 wt %. Certain of these embodiments contain two ormore such alkaline earth oxides in a range of 1 to 45 wt % cumulatively,such as in the range of 5 to 25 wt %.

The biocompatible materials of the invention are in the form of solidfibers, hollow fibers, ribbons, solid spheres, hollow spheres,particles, and combinations thereof. In an especially preferredembodiment for many applications, the composition is in the form of ascaffold body which includes fibers, and in certain such embodiments itis a scaffold body which consists essentially of components which arefibers. The fibers have an aspect ratio of at least 2:1length:transverse dimension (e.g., diameter), and more typically atleast 5:1, such as greater than 10:1. In certain embodiments of theinvention, the scaffold body components are primarily one form, such asfibers, in combination with a minor constituent of a second form fromthe foregoing options, such as microspheres.

There is also an option with this invention of employing distinctcomponent compositions to strategically impart certain properties. Forexample, the composition in some embodiments of the composition employs10 to 90 wt % of components having one composition selected from theabove, and 10 to 90 wt % of components of a different composition. Oreven more than two such types of components may be employed. That is,the material may contain at least 10 wt % of components comprising afirst component material within the contemplated compositions and atleast 10 wt % of components comprising a second component material,wherein the first and second component materials have compositionsmeasurably distinct from each other. And it is contemplated that onlythe first component material may contain Cu and/or other trace element,or that Cu may be present in both materials in different amounts. Thispermits the selection of, for example, faster reacting fibers incombination with slower reacting fibers; or the selection ofCa-containing fibers with Ca-free fibers. One can therefore selectstandard composition components and combine them with non-standardcomposition components to effectively customize or dope the scaffold forthe application presented, or for the host's particular needs.Alternatively, hollow spheres containing a growth factor or drug fordelivery to the host can be incorporated with other structuralcomponents, such as fibers.

In one embodiment the Cu and/or other trace element is incorporated intothe materials and a scaffold is formed to have a porosity which isselected to provide fluid flow into the scaffold to facilitate uptake ofbodily fluids, while maintaining sufficient strength for handling andimplantation. The porosity is between about 15 vol % and about 90 vol %.There are different levels of porosity, for example between about 15 andabout 30 vol %, or between about 30 and about 60 vol %, or between about60 and about 90%, which are preferred for different applications.Porosity depends on or is controlled by many factors such as fiberorientation, shape of particles or microspheres, and the thermaltreatment (time/temperature) used to bond the elements together.Independent of this bulk porosity, interconnectivity is also importantin embodiments of the invention which are in the form of scaffolds.Because tissue repair is strongly influenced by flow of bodily fluidsinto the scaffold, it is preferred to have a high level ofinterconnectivity of pores within the scaffold, and a low level ofclosed pores. That is, it is important that most pores be connected toother pores, and that there is a direct or indirect path from most poresto the exterior surface of the scaffold. In certain embodiments, atleast about 80 vol %, such as at least about 90%, of the pore volume ofthe scaffold is directly or indirectly through other pores accessiblefrom the scaffold exterior, and therefore accessible to bodily fluids.

The method of making the biocompatible materials is not narrowlycritical to the invention. By way of example, in preparing thebiocompatible materials, individual analytical reagent grade componentsare weighed, mixed thoroughly, and melted in a platinum crucible attemperatures between 1000 to about 1500° C., depending upon compositionfor approximately one to four hrs. The melt is then quenched, forexample, on a steel or copper plate to form glass that can be groundinto particulates of a desired size. The particulates can bespheroidized to form microspheres of a chosen diameter. The material ofpreferred composition when in the form of a melt can easily be formedinto fibers. If fibers of the borate glass are made, they can either bepulled by hand directly from the melt or pulled through bushing by arotating drum.

The components can be self bonded to form three dimensional scaffolds bysimply heating an assemblage of particulates in a furnace and allowingthe fibers/particles/spheres to soften and bond to each other. After theallotted time at temperature, the construct is removed from the furnaceand cooled to room temperature. Many prior biocompatible glasses, suchas 45S5, are difficult to self bond due to crystallization of the glass.Therefore the self-bonding ability of the borate glasses comprising Cuis a distinct advantage over other biocompatible materials currently inuse.

In one embodiment of the invention employing the Cu-containingbiocompatible materials the Cu-containing materials are in the form of atissue scaffold prepared from fibers which are aligned so that amajority of the fibers are substantially aligned in a paralleldirection. The scaffold is prepared by placing and orienting fibers in aunidirectional manner in a mold. The fibers in the mold are heated to atemperature where the fibers soften and bond together. In one preferredembodiment, the fibers are self bonded in the sense that no adhesive,braze, or other external bonding agent is used for bonding. Analternative embodiment employs a biocompatible agent or adhesive tofacilitate bonding, such that the fibers are not self bonded, at leastin part. Upon cooling, the assemblage of bonded fibers is sufficientlyrigid and strong that the assemblage can be removed from the mold andhandled. The scaffold is sufficiently rigid that it can be implantedinto a mammal where it facilitates the repair and regeneration of hardtissue such as bone (including cortical and cancellous) or soft tissuesuch as muscle, cartilage, skin, organ, or other hard or soft tissue.

The orientation of the fibers in a lengthwise direction in theself-bonded scaffold provides lengthwise channels (or connected pores)among the fibers, which channels provide for uptake into the scaffold ofstem cells, growth factors, medicines, red blood cells and other bodilyfluids and components carried in bodily fluids. The fibers are arrangedto define channels within the scaffold which facilitate fluid flow intoand lengthwise within the scaffold from one end to the other end. Theorientation also provides for channels in a transverse directiongenerally perpendicular to the lengthwise direction of the orientedfibers, to facilitate uptake of fluids from the outer surface of theinterior or core of the scaffold. These longitudinal and transversechannels exert significant capillary forces on a liquid which cause theliquid to be drawn into the scaffold. This capillary action facilitatesthe distribution of these fluids and components relatively uniformlythrough the scaffold and enables fluids to flow from one end of thescaffold to the other or to enter the scaffold from its surface andtransmit the liquid to its ends.

The invention in one embodiment employs fibers having a diameter, priorto molding and softening, between about 20 and about 5000 microns, suchas between about 50 and about 5000 microns. In one embodiment thescaffold is prepared from fibers having diameters between about 100 andabout 450 microns, such as between about 100 and about 300 microns. Inan alternative embodiment, the scaffold is prepared from fibers havingdiameters up to about 3000 or 5000 microns (3 to 5 mm), which can bedeemed more akin to rods than fibers in some contexts, but for purposesof the discussion of this invention fall within the definition of“fibers.”

In one aspect of the invention employing co-aligned fibers, at leastabout 75 or 85% by volume of the fibers in the scaffold arelongitudinally co-aligned. In this regard the fibers are co-alignedlongitudinally, where “co-aligned longitudinally” and the like phrases(e.g., “in lengthwise co-alignment”) as applied to a group of adjacent,bundled, or joined fibers in this application means that the alignmentof each fiber in the group at any one place along at least about 75% ofits length does not deviate more than about 25 degrees from parallel tothe central axis of the scaffold. In one preferred embodiment, eachfiber in the group at any one place along at least about 75% of itslength does not deviate more than about 15 degrees from parallel to thecentral axis of the scaffold. In another preferred embodiment, eachfiber in the group at any one place along at least about 75% of itslength does not deviate more than about 10 degrees from the central axisof the scaffold. So it is evident that this co-alignment aspect does notrequire 100% precise co-alignment of all fibers. The longitudinalco-alignment aspect also allows for some minor deviation of specificsegments of individual fibers to an orientation outside these 25, 15,and 10 degree requirements. This is reflected in the requirement thatthe longitudinal co-alignment is of each fiber along at least 75% of itslength, rather than necessarily along its entire length. So up to about25% of the length of an individual fiber may be misaligned because, forexample, it was bent during the scaffold-making process or otherwise.Each fiber in the scaffold is not absolutely straight, nor is it lyingalong an absolutely straight line strictly parallel to all other fibersin the scaffold. And each fiber is oriented generally in the samedirection, but each is not oriented in exactly the same direction.Moreover, the scaffold itself in certain embodiments is curved, bent, orotherwise not straight, in which cases the central axis of the scaffoldto which the alignment of the fibers is within 25 degrees of parallel isalso curved, bent, or otherwise not straight. In certain embodiments astraight or curved scaffold is machined into a more complex shape, inwhich instance the scaffold central axis refers to the central axis asmolded and prior to machining.

In order to allow capillary action and channel-forming, the scaffoldtheoretically contains at least three fibers, although the scaffoldtypically comprises dozens and even hundreds of fibers. The fibers liegenerally lengthwise of the scaffold central axis A (i.e., lie generallyin the direction of the central axis) and are generally free of helicalorientation about the scaffold central axis. This arrangement applies toat least about 75 vol % of the fibers and preferably to substantiallyall of the fibers.

The aspect of this embodiment that the fibers are co-alignedlongitudinally contemplates that the fibers are positioned so that theyhave a similar alignment, which similar alignment may be straight, bent,or curved. In most embodiments they are non-helical. In a separate anddistinct aspect of certain preferred embodiments, this common alignmentis limited to a generally straight alignment along at least about 75%,85%, or 95% of the length of the fibers. In other words, at least about75%, 85%, or 95% of each fiber is generally straight, i.e., at leastabout 75%, 85%, or 95% of the length of each fiber has an alignmentwhich is within 10 degrees of a mean straight central axis for thefiber. So up to 5%, 15%, or 25% of the length of each fiber may becurved, bent, or otherwise deviate more than 10 degrees from straight inrelation to the overall fiber length, but the rest of each fiber isgenerally straight in that it so deviates less than 10 degrees. In onepreferred embodiment, substantially the entire length of each fiber isgenerally straight in that it deviates less than 10 degrees from thefiber's average central axis. The “mean straight central axis” is theimaginary central axis for the fiber which is absolutely straight and isan average of all axes along the fiber length.

The fibers in the scaffold of these embodiments are selected to havecharacteristics suitable for the specific application. In oneembodiment, the fibers have a length between about 6 mm and about 150mm, such as between about 12 mm and about 100 mm or between about 25 mmand about 75 mm. Each fiber has a length which is at least about 10times its diameter. “Diameter” as used herein refers to the fiber'slargest dimension transverse to its length, and it does not imply thatthe fibers are perfectly circular in cross section. Each fiber thereforehas a fiber lengthwise dimension which is at least about 10 times thefiber transverse dimension, e.g., diameter. In one embodiment, the fiberlength is selected so that all, substantially all, or at least about 85vol % of the individual fibers extend the entire length of the scaffold.The fibers may be selected to have a pre-molding, pre-joining lengthwhich corresponds to the length of the scaffold. Or in most embodiments,the length of the fibers is longer than the desired ultimate scaffoldlength, and the scaffold is cut to the desired length after molding andjoining. In an alternative embodiment, the length of a substantialportion (e.g., at least 40 vol %) or all of the fibers is significantlyless than the entire length of the scaffold.

The scaffold in these embodiments is manufactured to have a sufficientlyhigh open and interconnected porosity from end to end of the scaffold tofacilitate capillary flow of fluids such as bodily fluids and medicinesand components they carry through the length of the scaffold, as well asgenerally transverse from outside walls of the scaffold into thescaffold interior in directions generally transverse to the longitudinaldimension of the fibers. And the scaffold is manufactured so that theultimate porosity is low enough that the scaffold has required strengthfor handling, implantation, and service after implantation. If theporosity is too high, the scaffold risks breakage in service, dependingon where it is implanted and the loads it encounters. In a preferredembodiment, the porosity as measured in volume is between about 10% andabout 35%, for example between about 10% and about 30%, or between about10% and about 25%. The porosity is controllable mainly by controllingthe degree of softening of the fibers, in that highly softened fibersfuse together more completely to a structure with lower porosity. Thedegree of softening and fusing is controlled by controlling the joiningtemperature and time. Porosity is also affected by the fiber diameterand by the range in fiber diameter within a given scaffold. Porositytends to increase with an increasing range in fiber diameter.

The biocompatible material may be glassy, glass ceramic, or ceramic innature. However the glassy state is preferred in this invention because,generally speaking, glassy materials are easier to form into differentshapes, bond at lower temperatures and are more chemically homogeneousthan their crystalline or partially crystalline counterparts of the samecomposition. It is therefore preferable that the biocompatible materialis substantially glass in that less than about 5 wt %, more preferableless than 1 wt %, of the component material is crystalline material.More particularly, it is preferable that there is less than 5 wt %,preferably less than 1 wt %, crystallization when the material is heatedto a temperature needed to bond the individual glass particles together.By way of example, in one embodiment it is preferable that there is lessthan 5 wt %, preferably less than 1 wt %, crystallization when thematerial is heated to 800° C. at an average heating rate of 20° C./min,held at that temperature for 10 minutes, then cooled to room temperatureby exposure to STP conditions of room temperature and atmosphericpressure. More preferably, the glass will contain less than 5 wt %crystallization, even more preferably less than 1 wt % crystallization,after being heated to 575° C. with a ramp rate of 20° C./min, and heldat that temperature for 20 minutes, then cooled to room temperature byexposure to STP conditions. The fibers used in many embodiments of theinvention, consistent with the foregoing description, are at least 99 wt% an amorphous or non-crystalline solid, for example made by fusing amixture of oxides such as one or more of SiO₂, B₂O₃, P₂O₅ (known asglass forming oxides) with basic oxides such as the alkali and alkalineearth oxides, along with the Cu compound. In an alternative embodiment,the fibers include glass ceramics fibers that contain both glassy andcrystalline regions which in many respects function in the same manneras a fiber that is completely (100%) non-crystalline. It is acceptablein some applications if the glass fiber crystallizes during the bondingstep. The fibers may alternatively be pre-reacted biocompatible glassessuch as glass fibers pre-reacted for example to have a thin surfacelayer of hydroxyapatite.

Example 1

Several borate-based glasses were prepared containing CuO in variousamounts according to the following concentrations:

Trace Element Doped Borate Biocompatible Glasses (wt %) Glass B₂O₃ Na₂OCaO K₂O MgO P₂O₅ CuO SrO ZnO Fe₂O₃ B3 53.00 6.00 20.00 12.00 5.00 4.00B3 Cu-1 52.95 5.99 19.98 11.99 5.00 4.00 0.10 B3 Cu-2 52.89 5.99 19.9611.98 4.99 3.99 0.20 B3 Cu-3 52.79 5.98 19.92 11.95 4.98 3.98 0.40 B3Cu-4 52.47 5.94 19.80 11.88 4.95 3.96 1.00 B3 Cu-5 51.94 5.88 19.6011.76 4.90 3.92 2.00 G 51.73 5.86 19.52 11.71 4.88 3.90 0.40 2.00 H51.20 5.80 19.32 11.59 4.83 3.86 0.40 2.00 1.00 I 50.88 5.76 19.20 11.524.80 3.84 0.40 2.00 1.00 0.40

Scaffolds prepared from glasses A, B, C, D, E, and F, which are depictedin FIG. 1, were implanted subcutaneously in the backs of rats, forselected time periods, and examined for vascularization. The rats wereFisher 344 rats having an age between 9 and 11 weeks and a weightbetween 200 and 300 grams. Prior to implantation, the scaffolds werewashed twice with ethyl alcohol and heat sterilized at 250° C. for 2.5hours in a small box furnace. For implantation, the back of the rat wasshaved, sterilized with iodine, and washed with 70% ethanol. Each ratwas anesthesized with a mixture of isofluorine and medical grade oxygen.Implantation was subcutaneously in a pocket formed in the back of eachrat. Each pocket was sufficiently large to ensure that each scaffoldcould be inserted away from the incision site. The incisions were closedwith super glue (Krazy® Glue, Elmers Products inc. Columbus, Ohio).After implantation, 0.1 mL of Penicillin G Procaine was injected intoeach thigh of the rat to prevent infection. The rats were placed on aheating pad in a cage with fresh air during recovery.

FIG. 2 shows the implanted scaffolds after two weeks; and FIG. 3 showsthe implanted scaffolds after four weeks. FIG. 4 shows the implantedscaffolds of B3 (no Cu), B3 Cu-1 (0.1 wt % CuO), and B3 Cu-3 (0.4 wt %CuO) after six weeks. The designation “w/MSC” refers to scaffolds seededwith 50,000 mesenchymal stem cells (msc), and “w/o MSC” designates noseeding. The effect of increasing Cu content on increasingvascularization was evident.

Example 2

The scaffolds seeded with 50,000 mesenchymal stem cells (msc) wereanalyzed after removal from the rat. The scaffolds were sectioned andstained for histology (H&E). The degree of vessel formation wasdetermined in 20 randomly selected spots throughout the sections, asindicated by the boxes in FIG. 5 (B3; no CuO), FIG. 6 (B3 Cu-1; 0.1 wt %CuO), and FIG. 7 (B3 Cu-3; 0.4 wt % CuO). FIG. 8 is a graph comparingtotal vascular area as a function of CuO concentration in the glass. Theglass containing no CuO had a total of 14000 μm² vascular area; theglass containing 0.1% CuO had a total of 16000 μm² vascular area; andthe glass containing 0.4% CuO had a total of 40000 μm² vascular area.There was a nearly 300% increase in vascular area in comparing the glasscontaining 0.4% CuO to the glass containing no CuO.

Example 3

Copper trace element release rates were calculated for the B3 Cu-3 (0.4wt % CuO) and B3 Cu-1 (0.1 wt % CuO) glasses. The scaffold mass was 70mg (0.070 g). So the scaffold having 0.4 wt % CuO contained 0.00028 gCuO/scaffold, which is equivalent to 0.00022 g Cu/scaffold. The numberof moles Cu was calculated as 0.00022 g/(63.55 g/mole), which equals3.52E-6 moles Cu. Assuming six weeks (42 days) for the scaffold tocompletely react, the rate of dissolution was 3.52E-6 moles Cu in 42days, which means 8.387E-8 moles of Cu was released or dissolved fromthe glass per day. The amount of new tissue grown was measured to be0.05 g tissue/scaffold. Based on Amer. J. Phys. 214, 1968, the bloodflow rate through adipose tissue of unanesthesized rats was a minimum of0.1 and to a maximum of 0.4 ml/min/gram of tissue.

B3 Cu-3 (0.4 wt % CuO)

The scaffold having 0.4 wt % CuO contained 0.00028 g CuO/scaffold, whichis equivalent to 0.00022 g Cu/scaffold. The number of moles Cu wascalculated as 0.00022 g/(63.55 g/mole), which equals 3.52E-6 moles Cu.Assuming a linear reaction rate over 42 days for the scaffold tocompletely release all copper, the Cu release rate was 8.387E-8moles/day. This is equivalent to 1.2E-6 moles of Cu/gram of glass/day.

B3 Cu-1 (0.1 wt % CuO)

Using a similar calculation for the B3 Cu-1 scaffold, the calculatedrelease rate for copper was 2.095E-8 moles/day. The equivalent rate is3.0E-7 moles of Cu/gram of glass/day.

The blood flow rates in rat subcutaneous adipose tissue have beenmeasured between 0.1 and 0.4 ml/min/gram and reported by Herd et. al. inBlood flow rates through adipose tissue of unanesthetized rats. Americanjournal of physiology, 1968. 214: p. 263-268. Using the Cu release ratesfor the B3 Cu-1 and B3 Cu-3 scaffolds described above, the Cuconcentrations of the rat bodily fluids were calculated. The calculatedvalues for the Cu concentration in the rat bodily fluids were in therange of Cu concentration of Cu doped cell culture mediums that promotedendothelial cell proliferation in-vitro reported by Hu et. al. in CopperStimulates Proliferation of Human Endothelial Cells Under Culture.Journal of Cellular Biochemistry, 1998. 69: p. 326-335 and increasedendothelial cell migration rates in-vitro reported as reported byMcAuslan et al. in Endothelial Cell Phagokinesis in Response to SpecificMetal Ions. Experimental Cell Research, 1980. 130: p. 147-157.

For the 0.4 wt % CuO scaffold at the minimum blood flow rate, the litersof flow through the scaffold was calculated as follows: 1440 min/day(0.1 ml/min*g)(1 day) (0.05 g)=7.2 ml=0.0072 L. Since there was a dailyrelease of Cu of 8.387E-8 moles into a blood flow of 0.0072 L, the rateof Cu release was calculated as 8.387E-8 moles/day Cu/0.0072 L=1.165E-5mol/L=11.65 micromolar Cu.

For the 0.4 wt % CuO scaffold at the maximum blood flow rate (4×0.0072L=0.0288 L), the rate of Cu release was calculated as 8.387E-8 moles/dayCu/0.0288 L=2.91 E-6 mol/L=2.91 micromolar Cu.

For the 0.1 wt % CuO scaffold at the minimum blood flow rate (0.0072 L),the rate of Cu release was calculated as 2.095E-8 moles/day Cu/0.0072L=2.91E-6 mol/L=2.91 micromolar Cu.

For the 0.1 wt % CuO scaffold at the maximum blood flow rate (4×0.0072L=0.0288 L), the rate of Cu release was calculated as 2.095E-8 moles/dayCu/0.0288 L=7.3E-7 mol/L=0.73 micromolar Cu.

Example 4

A blended fiber scaffold was prepared from a 50:50 by weight mixture offibers of two or more distinct compositions:

Fiber Content Glass (wt %) B₂O₃ Na₂O CaO K₂O MgO P₂O₅ CuO Glass A 5053.00 6.00 20.00 12.00 5.00 4.00 0.0  Glass B 50 52.47 5.94 19.80 11.884.95 3.96 1.00

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above compositions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

1. A scaffold for implantation into a mammal to facilitate vessel growthin repair, regeneration, and/or proliferation of bodily tissue, thescaffold comprising: a scaffold body of biocompatible material in aphysical form selected from the group consisting of fibers, hollowfibers, tubes, ribbons, solid spheres, hollow spheres, particles, bondedparticles, and combinations thereof; wherein the biocompatible materialcomprises from about 40 to about 80 wt % B₂O₃; and wherein thebiocompatible material comprises one or more trace elements selectedfrom the group consisting of Cu, Fe, Sr, and Zn in a concentrationbetween about 0.05 and 10 wt % per trace element chemically dissolved inthe biocompatible material.
 2. The scaffold of claim 1 wherein thebiocompatible composition comprises: from about 40 to about 80 wt %B₂O₃; one or more alkali oxides selected from the group consisting ofLi₂O, Na₂O, K₂O, and Rb₂O; and one or more alkaline earth oxidesselected from the group consisting of MgO, SrO, BaO, and CaO.
 3. Thescaffold of claim 1 wherein the biocompatible composition comprises:from about 40 to about 80 wt % B₂O₃; from about 1 to about 50 wt % ofone or more alkali oxides selected from the group consisting of Li₂O,Na₂O, K₂O, and Rb₂O; and from about 1 to about 50 wt % of one or morealkaline earth oxides selected from the group consisting of MgO, SrO,BaO, and CaO.
 4. The scaffold of claim 1 wherein the biocompatiblecomposition comprises: from about 40 to about 80 wt % B₂O₃; from about 5to about 20 wt % of one or more alkali oxides selected from the groupconsisting of Li₂O, Na₂O, K₂O, and Rb₂O; and from about 5 to about 40 wt% of one or more alkaline earth oxides selected from the groupconsisting of MgO, SrO, BaO, and CaO.
 5. The scaffold of claim 1 whereinthe biocompatible composition comprises: from about 40 to about 80 wt %B₂O₃; one or more alkali oxides selected from the group consisting ofLi₂O, Na₂O, K₂O, and Rb₂O; one or more alkaline earth oxides selectedfrom the group consisting of MgO, SrO, BaO, and CaO; and Cu in aconcentration between about 0.1 and about 2.5 wt %.
 6. The scaffold ofclaim 1 wherein the biocompatible composition comprises: from about 40to about 80 wt % B₂O₃; one or more alkali oxides selected from the groupconsisting of Li₂O, Na₂O, K₂O, and Rb₂O; one or more alkaline earthoxides selected from the group consisting of MgO, SrO, BaO, and CaO; andFe in a concentration between about 0.05 and about 5 wt %.
 7. Thescaffold of claim 1 wherein the biocompatible composition comprises:from about 40 to about 80 wt % B₂O₃; one or more alkali oxides selectedfrom the group consisting of Li₂O, Na₂O, K₂O, and Rb₂O; one or morealkaline earth oxides selected from the group consisting of MgO, SrO,BaO, and CaO; and Sr in a concentration between about 0.05 and about 5wt %.
 8. The scaffold of claim 1 wherein the biocompatible compositioncomprises: from about 40 to about 80 wt % B₂O₃; one or more alkalioxides selected from the group consisting of Li₂O, Na₂O, K₂O, and Rb₂O;one or more alkaline earth oxides selected from the group consisting ofMgO, SrO, BaO, and CaO; and Zn in a concentration between about 0.05 andabout 5 wt %.
 9. A scaffold for implantation into a mammal to facilitatevessel growth in repair, regeneration, and/or proliferation of bodilytissue, the scaffold comprising: a scaffold body comprisingbiocompatible material in a physical form selected from the groupconsisting of fibers, hollow fibers, tubes, ribbons, solid spheres,hollow spheres, particles, bonded particles, and combinations thereofwhich biocompatible material comprises a glass former selected from thegroup consisting of B₂O₃, SiO₂, P₂O₅, and combinations thereof, andwhich is biodegradable in mammalian bodily fluids; and one or more traceelements from the group consisting of Cu, F, Fe, Mn, Mo, Ni, Sr, and Znin a concentration between about 0.05 and 10 wt % per trace elementchemically dissolved in the biocompatible material; wherein said glassformers are concentration balanced to impart a biodegradability suchthat at least about 20 wt % of the biocompatible material biodegradeswithin six weeks of subcutaneous implantation in a Fisher 344 rat havingan age between 9 and 11 weeks and a weight between 200 and 300 grams, asdetermined by testing on rats with a standard deviation of 25%(relative) of the biocompatible material weight and a population size of10.
 10. The scaffold of claim 9 wherein the composition is in the formof fibers or bonded particles.
 11. The scaffold of claim 9 wherein thecomposition comprises no more than 0.1 weight % Ca.
 12. The scaffold ofclaim 9 wherein the biocompatible material does not convert tobone-precursor calcium phosphate compounds in phosphorus-containingmammalian fluids.
 13. The scaffold of claim 9 wherein said one or moretrace element is selected from the group consisting of Cu, Fe, Sr, andZn.
 14. The scaffold of claim 13 wherein the composition is in the formof fibers or bonded particles.
 15. The scaffold of claim 13 wherein thecomposition is in the form of fibers or bonded particles and the traceelement is Cu in a concentration between about 0.05 and 5 wt %.
 16. Thescaffold of claim 13 wherein the trace element is Cu in a concentrationbetween about 0.05 and 5 wt %.
 17. The scaffold of claim 13 wherein thetrace element is Cu in a concentration between about 0.05 and about 5 wt%, wherein the composition is in the form of fibers, and wherein thescaffold has a trace element release rate of between about 0.5 and about100 E-7 moles of Cu, per gram of glass, per day.
 18. The scaffold ofclaim 13 wherein the biocompatible composition comprises: from about 40to about 80 wt % B₂O₃; one or more alkali oxides selected from the groupconsisting of Li₂O, Na₂O, K₂O, and Rb₂O; one or more alkaline earthoxides selected from the group consisting of MgO, SrO, BaO, and CaO; andCu in a concentration between about 0.1 and about 2.5 wt %.
 19. Thescaffold of claim 13 wherein the biocompatible composition comprises:from about 40 to about 80 wt % B₂O₃; one or more alkali oxides selectedfrom the group consisting of Li₂O, Na₂O, K₂O, and Rb₂O; one or morealkaline earth oxides selected from the group consisting of MgO, SrO,BaO, and CaO; and Fe in a concentration between about 0.05 and about 5wt %.
 20. The scaffold of claim 13 wherein the biocompatible compositioncomprises: from about 40 to about 80 wt % B₂O₃; one or more alkalioxides selected from the group consisting of Li₂O, Na₂O, K₂O, and Rb₂O;one or more alkaline earth oxides selected from the group consisting ofMgO, SrO, BaO, and CaO; and Sr in a concentration between about 0.05 andabout 5 wt %.
 21. The scaffold of claim 13 wherein the biocompatiblecomposition comprises: from about 40 to about 80 wt % B₂O₃; one or morealkali oxides selected from the group consisting of Li₂O, Na₂O, K₂O, andRb₂O; one or more alkaline earth oxides selected from the groupconsisting of MgO, SrO, BaO, and CaO; and Zn in a concentration betweenabout 0.05 and about 5 wt %.
 22. A scaffold for implantation into amammal to facilitate vessel growth in repair, regeneration, and/orproliferation of bodily tissue, the scaffold comprising: a scaffold bodycomprising biocompatible material in a physical form selected from thegroup consisting of fibers, hollow fibers, tubes, ribbons, solidspheres, hollow spheres, particles, bonded particles, and combinationsthereof which biocompatible material comprises a glass former selectedfrom the group consisting of B₂O₃, SiO₂, P₂O₅, and combinations thereof,and which is biodegradable in mammalian bodily fluids; one or more traceelements from the group consisting of Cu, F, Fe, Mn, Mo, Ni, Sr, and Znin a concentration between about 0.05 and 10 wt % per trace elementchemically dissolved in the biocompatible material; wherein thebiocompatible material does not convert to bone-precursor calciumphosphate compounds in phosphorus-containing mammalian fluids.
 23. Amethod for facilitating vessel growth in repair, regeneration, and/orproliferation of bodily tissue in a mammal comprising implanting thescaffold of claim 9 into the mammal.